This invention relates to improvements in thermal analysis instruments equipped with a cooling mechanism.
A conventional thermal analysis instrument equipped with a cooling mechanism is disclosed in Japanese Patent Application Laid-Open No. 116744-02 and has a structure as shown in FIG. 6 of the drawings of the present application. In particular, the thermal analysis instrument, in particular a differential scanning calorimeter or a differential thermal analyzer, includes a controller 1 coupled to a heating furnace 2. A housing 11 of heat insulating material is formed around the sides of heating furnace 2 to form a closed space 8 between housing 11 and the sides of furnace 2. Cool air 54 is admitted into this chamber 11 and heated air 57 leaves chamber 11 via a passage 55. An opening is formed at the upper end of heating furnace 2 to permit a sample to be inserted into and withdrawn from furnace 2. A removable cover or the like is frequently put in this opening.
This cover or the like is installed to form a closed space around the sample placed inside heating furnace 2 to prevent the sample from being affected or disturbed by the outside air during measurements.
In recent years, some analysis instruments of this kind have often been equipped with a robot mechanism such as an automatic sampler to automate replacement and placement of samples. Numerous samples are successively subjected to measurement automatically.
Especially where a robot mechanism of this type is mounted to a thermal analysis instrument to attain automation, it is inevitable that a cooling mechanism is mounted to the heating furnace 2, because it is necessary to elevate and lower the temperature of the sample.
The heating furnace 2 of the conventional thermal analysis instrument equipped with a cooling mechanism has an open top portion and, therefore, the aforementioned robot mechanism such as an automatic sampler is especially adapted to be mounted to the instrument, for replacement and placement of the sample.
When a measurement is made with the instrument of this structure using a cooling refrigerant, if the temperature at the upper end of the heating furnace 2 becomes lower than the dew point of the atmosphere around the top portion of the furnace 2, then dew condensation occurs at the upper end portion of the furnace, because the upper end portion is in contact with the atmosphere.
Dew condensation takes place as long as the upper end of the heating furnace 2 is in contact with the open atmosphere. More dew condensation occurs as the temperature inside the furnace 2 drops, as the furnace 2 is kept at low temperatures for a longer time, and as the moisture content of the atmosphere increases, i.e. as the dew point increases.
When the temperature at the upper end structure of the heating furnace is low, the dew produced by the condensation becomes frost and deposits at the upper end of the furnace 2.
After a measurement, the robot mechanism removes the cover or the like placed at the upper end of the heating furnace 2 to replace the sample. At this time, the cover or the like and the opening at the upper end of the furnace 2 become frozen because of the frost deposited at the upper end of the furnace 2, including the cover or the like. This makes it impossible to remove the cover or the like.
Where it is essential for measurement that the temperature inside the heating furnace 2 be lowered, it is customary to add a closed space to the vicinities of the top portion of the furnace 2 to prevent the top portion of the furnace 2 from touching the open air, for preventing deposition of frost due to the aforementioned dew condensation.
In this case, however, if a robot mechanism is added to the instrument, it is necessary to open the added closed space by operation of the robot mechanism during replacement of the sample. Hence, a new function must be imparted to the robot mechanism. This represents a decided drawback.